CAM software systems are used to program computer numerical control (CNC) machine tools that are used in machine shops for the production of discrete parts such as molds, dies, tools, prototypes, and aerospace components. The variety of shapes that can be machined is nearly infinite: shapes are usually classified according to convenient mathematical structures, often involving the use of sub-fields of mathematics, e.g., topology.
A “channel” shape is a simple primitive geometric concept, familiar also to non-technicians. A simple and intuitive description of a channel may be done by specifying a left lateral wall and a right lateral wall whose baselines are joined by a bottom surface. Such a shape occurs in most of the parts being dealt with in the CAM production environment; in particular, there is a wide variety of channel shapes in the specific area of production of gears, impellers, propellers, pumping and moving devices, and blisks—types of compressors obtained by the junction of blades and disks. The different channels may differ, one from another, with respect to: height of the walls, curvature of the wall surfaces and of the bottom surface, relative position of the walls, constant or non-constant width of the channel, thickness of the wall surfaces, and other geometric parameters.
The milling of such channels may be a delicate process where several mechanical, and geometric constraints may need to be taken into account. Manufacturing a design surface by a numerically controlled (NC) machine may comprise two stages: a rough cutting and a finish machining.
During the rough cutting, the raw material must be removed as fast as practicable while ensuring neither excessive cutting nor gouging, i.e., where the cutting tool removes a portion of rough material that is instead required to belong to the final targeted shape, introducing thereby an irreparable mistake or blemish into the entire milling process. Moreover, the rate of contact between the cutting tool and the rough material to be removed cannot exceed a prescribed threshold; a threshold which depends on the shape of the cutter end, i.e., usually flat, spherical or torical—the latter being an intermediate shape between the first two, and on the type of rough material being removed.
During the finish machining, the tool may be placed so as to have the maximal contact with the surface so as to remove the remaining excess and create a well-finished and accurate surface. In both stages, i.e., the rough cutting stage and the finish machining stage, the possible onset of vibrations and motion instability of the cutting tool, also termed chatter in the CAM Lexicon, must be kept under control in order to reduce the mechanical pressure on the channel walls; walls that may be very thin—a particularly important consideration for channels having deep cavities.